package org.ecloud.utils;

import java.math.BigInteger;
import java.security.SecureRandom;
import java.util.Random;
import java.util.UUID;
import java.util.concurrent.locks.ReentrantLock;

/**
 * Helper for creating random and Type 1 (time-based) UUIDs.。
 * 
 */
public class UUIDUtil {

	private static boolean isThreadlocalRandomAvailable = false;
	private static Random random;
	private static final long LEAST_SIG_BITS;
	private static final ReentrantLock lock = new ReentrantLock();
	private static long lastTime;

	static {
		try {
			isThreadlocalRandomAvailable = null != UUIDUtil.class
					.getClassLoader().loadClass(
							"java.util.concurrent.ThreadLocalRandom");
		} catch (ClassNotFoundException ignore) {
		}

		byte[] seed = new SecureRandom().generateSeed(8);
		LEAST_SIG_BITS = new BigInteger(seed).longValue();
		if (!isThreadlocalRandomAvailable) {
			random = new Random(LEAST_SIG_BITS);
		}
	}

	private UUIDUtil() {
	}

	/**
	 * Create a new random UUID.
	 * 
	 * @return the new UUID
	 */
	public static UUID random() {
		byte[] randomBytes = new byte[16];
		if (isThreadlocalRandomAvailable) {
			java.util.concurrent.ThreadLocalRandom.current().nextBytes(
					randomBytes);
		} else {
			random.nextBytes(randomBytes);
		}

		long mostSigBits = 0;
		for (int i = 0; i < 8; i++) {
			mostSigBits = (mostSigBits << 8) | (randomBytes[i] & 0xff);
		}
		long leastSigBits = 0;
		for (int i = 8; i < 16; i++) {
			leastSigBits = (leastSigBits << 8) | (randomBytes[i] & 0xff);
		}

		return new UUID(mostSigBits, leastSigBits);
	}

	/**
	 * Create a new time-based UUID.
	 * 
	 * @return the new UUID
	 */
	public static UUID create() {
		long timeMillis = (System.currentTimeMillis() * 10000) + 0x01B21DD213814000L;

		lock.lock();
		try {
			if (timeMillis > lastTime) {
				lastTime = timeMillis;
			} else {
				timeMillis = ++lastTime;
			}
		} finally {
			lock.unlock();
		}

		// time low
		long mostSigBits = timeMillis << 32;

		// time mid
		mostSigBits |= (timeMillis & 0xFFFF00000000L) >> 16;

		// time hi and version
		mostSigBits |= 0x1000 | ((timeMillis >> 48) & 0x0FFF); // version 1

		return new UUID(mostSigBits, LEAST_SIG_BITS);
	}
	
	private static final SecureRandom secureRandom = new SecureRandom();
	
	/**
	 * 封装JDK中间无-分割.
	 */
	public static String uuid() {
		return create().toString().replaceAll("-", "");
	}
	
	/**
	 * 使用SecureRandom随机生成Long. 
	 */
	public static long randomLong() {
		return Math.abs(secureRandom.nextLong());
	}
}
